The disclosure relates generally to a scanning system, and more particularly concerns the correcting of illumination defects.
Conventional automatic duplex documents sheet handling and imaging systems have increased the effective imaging, scanning, or copying rate for both sides of sets of duplex documents. Such conventional automatic document handlers automatically sequentially feed and image a set or job of plural duplex document sheets, while at the same, these conventional document handlers are capable of feeding and copying simplex documents. A variety of systems and methods are conventionally used in the scanning operation. In a typical scanning operation, light from the scanner illuminates the surface of an original document and the document moving past an image sensor detects the intensity of light reflected from each location in the image and stores it as a proportionate electrical charge at a corresponding pixel location. Various exemplary scanning devices employ stationary Full-Width Imager Arrays (FWA) or linear Charge-Coupled Device (CCD) arrays. In such systems in which the imaging arrays are stationary, the arrays are often separated from the image to be scanned by a platen glass or other transparent surface or lens overlying the imaging array.
Document handlers employ various exemplary methods to move the original document to the transparent surface. One such exemplary method, commonly referred to as Constant Velocity Transport (CVT) scanning, employs a belt, roll, drum or other like device to move the image substrate to be scanned across a linear sensor, such as, for example, a Full-Width Imager Arrays (FWA). One or more scanners, printers, video displays and/or computer storage devices are often connected via a communications network, thereby providing a digital reproduction system. For example, a digital copier may incorporate a scanner and a digital printer.
A difficulty in such systems is that any defect or imperfection is repeatedly scanned and digitized. One such difficulty encountered in document handlers when the lead or trail edge of a document passes past the imaging sensor in a scanner. When the edges of the paper pass over the edge guide near the constant velocity transport (CVT) roll, the paper springs away from the normal path. The resulting change in illumination angle or integrating cavity effect (ICE) causes a lightness change near the edge of the document. When the document is reproduced, the output image will include a change in light level leading to a visual lightness defect corresponding with the position of the imperfection.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for correction of lightness change during the scanning operation.